Depends on what you're looking for. As they're both non-res and take Glock mags, and both lob a 9mm pistol round downrange, it'll boil down to what You would prefer in a carbine.
Sub-2000: Pros: Really cool folding option, comes with sights, is less money, possibly lefty friendly (? I haven't handled one myself). Cons: Doesn't accept optics easily, and the folding option is lost when they're mounted. Limited accessorizing (if you're into that).
JR Carbine: Pros: Kinda mimics an AR, takes standard AR furniture and trigger & fire control parts, easy to accessorize (if you're into that), integral flat top rail for sights/optics. Multi-caliber option will be available. Can be converted to be lefty friendly if that might matter. Cons: More money than the Kel-tec, no sights included, doesn't fold up, needs aftermarket ambi-safety for left handers, handguard is ugly (

).
Totally different carbines as far as I'm concerned, so it'll really come down to what matters to you. There are quite a few reviews on the Kel-tec online to give you a good idea of what they're about, but only a couple on the JR.
Decide what you want/need, buy it up and go shooting!